1. Field of the Invention
The present invention relates to a rotary torque detecting device mainly used for detection of rotary torque of a steering member of an automobile.
2. Description of the Related Art
In recent years, while automobiles are gaining higher functionality, rotary torque and rotation angle of a steering member are detected by using various rotary torque detecting devices and rotation angle detecting devices to carry out various controls of a vehicle such as controls of a power steering device and a brake device.
Such a prior-art rotary torque detecting device will be described with reference to FIGS. 19 and 20. FIG. 19 is a sectional view and FIG. 20 is an exploded perspective view of a prior-art rotary torque detecting device. In these drawings, substantially cylindrical first rotating body 1 rotates in synchronization with a steering member. Substantially arc-shaped magnet 2 has a north pole and a south pole formed to take up an angle of about 20° to 40°. Multiple magnets 2 are secured to a lower end of an outer periphery of first rotating body 1 and first rotating body 1 is covered with substantially cylindrical retaining body 3.
Substantially cylindrical second rotating body 4 is disposed below first rotating body 1. Substantially cylindrical first magnetic body 5 such as a permalloy has multiple protruding portions 5A formed on its inner periphery and second magnetic body 6 similarly has multiple protruding portions 6A on its inner periphery. First magnetic body 5 and second magnetic body 6 face magnets 2 through spacer 7 and are respectively secured to an upper end of substantially cylindrical second rotating body 4.
Multiple wiring patterns (not shown) are formed on upper and lower surfaces of wiring board 8 horizontally disposed beside first rotating body 1 and second rotating body 4. Furthermore, to a surface facing magnets 2, magnetic detecting element 9, such as a Hall element, disposed between first magnetic body 5 and second magnetic body 6 is attached.
On wiring board 8, control means 10 connected to magnetic detecting element 9 is formed of an electronic component such as a microcomputer. Furthermore, between first rotating body 1 and second rotating body 4, substantially columnar connecting body 11 such as a torsion bar having an upper end secured to first rotating body 1 and retaining body 3 and a lower end secured to second rotating body 4 by pins (not shown) is provided.
In substantially box-shaped upper case 12 and lower case 13 made of insulating resin, first rotating body 1, second rotating body 4, first magnetic body 5, second magnetic body 6, wiring board 8, and the like are housed. Furthermore, upper ends of first rotating body 1 and retaining body 3 rotatably protrude through an opening hole in an upper surface of upper case 12 and a lower end of second rotating body 4 rotatably protrudes through an opening hole in a lower surface of lower case 13 to form a rotary torque detecting device.
This rotary torque detecting device is mounted below a steering wheel of an automobile together with a rotation angle detecting device with a steering shaft attached to first rotating body 1 and second rotating body 4. Control means 10 is connected to an electronic circuit (not shown) of an automobile main body via a connector, a lead, and the like (not shown).
In the structure described above, if the steering wheel is turned, first rotating body 1 rotates. After connecting body 11 is twisted, second rotating body 4 rotates after a short lag behind first rotating body 1. At this time, however, the lag in rotation of second rotating body 4 behind first rotating body 1 is short during traveling of a vehicle, because rotary torque is small. The lag in rotation of second rotating body 4 is long during stoppage of the vehicle, because the rotary torque is large.
At this time, the lag in the rotation of second rotating body 4 behind first rotating body 1 is about 1° in terms of angle when the rotary torque is small and is about 4° when the rotary torque is large.
As first rotating body 1 and second rotating body 4 rotate, magnets 2 secured to them rotate and first magnetic body 5 and second magnetic body 6 rotate as well after a short lag. Then, magnetic detecting element 9 detects, through protruding portions 5A and 6A of first magnetic body 5 and second magnetic body 6, changes in magnetism of the north poles and the south poles of magnets 2 formed at predetermined intervals and inputs them to control means 10.
At this time, the magnetism detected by magnetic detecting element 9 is weak when the lag in the rotation of second rotating body 4, to which first magnetic body 5 and second magnetic body 6 are secured, behind first rotating body 1, to which magnets 2 are secured, is short and is strong when the lag in the rotation is long.
Then, control means 10 calculates the rotary torque of the steering member based on an intensity of the magnetism detected by magnetic detecting element 9 through first magnetic body 5 and second magnetic body 6 and outputs it to the electronic circuit of the automobile main body. The electronic circuit computes the rotary torque, the rotation angle of the steering member, or various data from speed sensors and the like attached to respective portions of a vehicle body to carry out various controls of the vehicle such as controls of a power steering device and a brake device.
In other words, if the vehicle is traveling and the rotary torque of the steering member is small, for example, effect of the power steering device is reduced and the steering wheel is turned with some degree of strong force. In other words, during stoppage of the vehicle when the rotary torque of the steering member is large, the effect of the power steering device is enhanced so that the steering wheel can be turned with small force.
As a technique related to the invention of the application, there is that disclosed in Unexamined Japanese Patent Publication No. 2008-82826, for example.
However, to produce each of first magnetic body 5 and second magnetic body 6 by using relatively expensive material such as a permalloy in the prior-art rotary torque detecting device, a central portion is punched first, the entire material is formed into a substantially cylindrical shape by deep drawing or the like, and multiple protruding portions 5A or 6A are formed at the inner periphery. Therefore, the production takes a lot of trouble, yields are low, and the device becomes expensive.
The present invention solves such conventional problems and it is an object thereof to provide a rotary torque detecting device having an inexpensive structure and capable of reliably detecting rotary torque.